Method and device for guiding a laser beam over an object

ABSTRACT

A system and method are provided for guiding a laser beam over a series of identical objects which can have varying arrangement relative to conveying and cutting apparatus. The present invention uses image position data to calculate deviations in position between a reference image and subsequent images, and to correct the cutting instructions based upon same.

BACKGROUND OF THE INVENTION

The invention relates to a method and an apparatus for guiding a laserbeam over an object from a plurality of identical objects, which areguided past the laser step by step in a conveying direction of theobjects, substantially periodically and with a varying arrangementrelative to the conveying direction, and are to be struck by the laserbeam at coincident locations. In particular, the invention relates to anapparatus and a method for cutting labels out of a strip-like textile,the labels being arranged in a varying manner relative to thelongitudinal or conveying direction of the labels.

Labels for textiles are produced by weaving companies and are normallypresent as a textile strip which has labels at substantially regularintervals, said labels containing information about a textile to beprovided with the label, such as washing instructions, information aboutmaterials and clothing size. The label identification can be carried outeither during the weaving operation by using threads of different colorsor by printing on the textile strip.

In such label textile strips, the labels are not always at the samespacing from one another in the longitudinal direction of the textilestrip. Furthermore, the labels may have angular positions with respectto the longitudinal direction of the textile strip. It is likewisepossible that the labels are offset at right angles to one another inrelation to the longitudinal direction of the textile strip.

It is known to guide the textile strip carrying the labels step by steppast a laser cutting device by means of a transport device whichcomprises a stepping motor, each label dwelling in the laser operatingarea for a suitable time period for the cutting operation. However,before the labels are cut out of the textile strip, it must beestablished which section of the textile strip which comprises the labelis to be cut out by the laser.

For this purpose, hitherto scissors have been used to cut a label fromthe textile strip by hand. By means of a scanner, an image of the labelis produced and displayed on a display device. The display device isconnected to a conventional computer which, for example, has cursorcontrol. The cursor, moved by a mouse, is used to make a mark in theimage of the label cut out by hand, along which the laser is to cutduring the cutting operation. The image provided with the mark andrelating to the label cut out by hand and to be designated as thereference object, is stored on a commercially available floppy disk. Asequence control system for the cutting operations of the laser makesaccess to the information on the floppy disk, so that labels guided stepby step past the laser are in each case cut out accordingly by thelaser.

However, this method of cutting labels out of a textile strip has thedisadvantage that, given a coincident advance of the textile stripbetween two cutting operations, varying spacings between two adjacentlabels are not taken into account, so that textile pieces which containonly part of the label can be cut out of the textile strip. As a remedy,provision has been made to provide the textile strips with a coloredmark, which is arranged in front of the label at a coincident spacing inthe conveying direction of the textile strip. By means of a colored-markreader, it is determined whether a label is located at a suitableposition for the laser cutting operation. However, this procedure hasthe disadvantage that positional changes between the labels with respectto the angular position of the labels and an offset at right angles tothe conveying direction of the labels are not taken into account.

The problem described by using the example of cutting labels out of atextile strip arises in principle in all methods and apparatuses inwhich a laser beam is guided over an object from a plurality ofidentical objects which pass a laser beam operating region one afteranother. The problem can also occur in laser labeling.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of further developing amethod and an apparatus of the type mentioned at the beginning in such away that, in the case of each of the objects, the laser beam is guidedsubstantially over the same locations of the object.

This object is achieved by a method of guiding a laser beam over anobject from a plurality of identical objects, which are guided past thelaser step by step in a conveying direction of the objects,substantially periodically and with a varying arrangement relative tothe conveying direction, and are to be struck by the laser beam atcoincident locations, the method comprising the following steps:

a) arranging a reference object in the image plane of an optical camera;

b) recording an image of the reference object by means of the camera anddisplaying the image on a display device;

c) marking a point or a line which is to be struck by the laser beam onthe image;

d) storing the reference object position data and the mark position datain a first memory;

e) arranging a further object in the image plane of the camera;

f) recording an image of the further object with the camera;

g) storing the object position data of the further object in a secondmemory;

h) calculating the deviation between the reference object position datain the first memory and the object position data of the further objectin the second memory;

j) calculating the laser position(s) relative to the further object onthe basis of the deviation in such a way that the laser strikes thefurther object at the positions marked in step c); and

k) guiding the laser over the further object to the/along the laserpositions calculated in step j).

According to the method, provision is therefore made firstly to recordan image of a reference object and, on this image, to mark a mark of thelocation of an object, for example points or lines, which are to bestruck by the laser beam. In order to record the reference image bymeans of the optical camera, the previously required cutting of areference label out by hand, which has to be scanned by a scanner, isdispensed with. The object or the label which serves as a reference canremain on the textile strip, so that the textile strip as a whole can bemoved immediately onto a transport device in order to carry out repeatedcutting operations.

After the position data of the reference label and the mark have beenstored, a desired number of labels can be cut out by the laser. Beforeeach cutting operation, first of all a video image of the current objectis recorded by means of the camera and local deviations between thecurrent object and the reference object are calculated. These calculateddeviations are used to control the laser.

For the example of cutting labels out of a textile strip, the result, ascompared with the prior art, has the advantage that label wastageresulting from faulty cutting of the labels, for example where part ofthe identification is lost, is reduced by about 10 to 20%. Similaradvantages result in the case of other methods in which a laser beam isto be guided over a plurality of objects. This applies in a particularfor any objects which are conveyed on a transport belt above which alaser is arranged for cutting or other purposes.

In order to repeat a laser guiding operation, method steps e)-k) arecarried out repeatedly.

If the objects are labels on a textile strip, the textile strip can bedriven by a stepping motor, controlled by a stepping motor controlsystem. The effect of the stepping motor is that the labels are guidedone after another into the operating region of the laser, which islocated in the spatial angle observed by the camera. Depending on theresults of the calculation of the position deviations between referencelabel and current label, the laser, which is controlled by a lasercontrol system, cuts the current label out of the textile strip.

In each step e), the stepping motor control system can be triggered by asignal from the laser control system which reproduces the completion ofstep k), so that the stepping motor drives the textile strip for apredetermined advance, for example 10 cm, so that the respectivelyfollowing label should lie in the laser operating region. The cameraspatial angle should be such that it covers the usual deviations of thelabels from a spatial angle central position. However, it is notpossible to completely rule out the situation in which labels arelocated only partly within the spatial angle of the camera. In thiscase, the performance of the method can be stopped and a fault messagecan be output.

Each step f) can be triggered by a signal from the stepping motorcontrol system, which reproduces the completion of stop e), to a cameracontrol system. This results in the image of the current label beingrecorded as soon as the label has reached a rest position.

The subject of the invention is additionally an apparatus for guiding alaser beam over an object from a plurality of identical objects, whichare guided past the laser step by step in a conveying direction of theobjects, substantially periodically and with a varying arrangementrelative to the conveying direction, and are to be struck by the laserbeam at coincident points, comprising:

a transport device for guiding the objects into the laser operatingregion,

a camera whose spatial angle covers the laser operating region,

a memory for storing images read out by the camera,

a display device for displaying the object images from the camera,

a marking device for marking a point or a line which is to be struck bythe laser beam on an object image.

a computing unit for calculating deviations between various objectimages from the camera and

a control unit for driving the laser on the basis of the results fromthe computing unit.

The invention will be described in more detail below using an exemplaryembodiment.

BRIEF DESCRIPTION OF DRAWINGS

The single FIGURE shows an overview of an apparatus for guiding a laserbeam over a plurality of identical objects.

DETAILED DESCRIPTION

The apparatus comprises a laser 1, a stepping motor 2 and a CCD camera3, which are all controlled by a computer 4 as a sequence controlsystem. The computer 4 is connected to a monitor 5.

A video image of an object, recorded by the camera 3, is read out by thecomputer 4 and displayed on the monitor 5. For example, the computer 4can be equipped with a mouse whose position is displayed on the monitoras a cursor. By actuating the mouse, a mark may be made in the videoimage displayed on the monitor 5. A reference image of an object,provided with the mark, is stored in a section of the memory of thecomputer 4.

After this procedure has been completed, in the case in which theapparatus is used for cutting labels from a textile strip, thecontinuous operation is initiated. First of all, the computer 4 sends asignal to the stepping motor 2, so that the next label, that is to saythe label which follows the reference label, passes into the spatialangle of the camera 4. After the next label has assumed a rest position,the stepping motor 2 sends a signal to the computer 4 which reproducesthe completion of the advance step for the label. The computer 4 thendrives the camera 3 so that an image of the object located in thespatial angle of the camera is recorded. The camera image is read outand stored by the computer. The computer 4 then calculates positionaldeviations of the reference label from the label just recorded. Thesedeviations include angular deviations relative to the longitudinaldirection of the textile strip, lateral offset at right angles to thelongitudinal direction of the textile strip, and offset in the directionof the textile strip. The data obtained by the calculation is used tocalculate the positions at which the marks defined in the referenceimage are located in the image of the current label.

The calculated positions of the marks in the current image are used bythe computer 4 for controlling the position of the laser 1. The cuttingoperation by means of the laser 1 then takes place. As soon as thecutting operation of the laser 1 has been completed, the laser 1 outputsa signal to the computer 4 which reproduces the completion of thecutting operation. By means of the computer 4, this signal triggersfurther actuation of the stepping motor 2. The further sequence of themethod is repeated in any desired number.

In order to prepare the laser cutting operations, data about the spacingto be expected between two labels on the textile strip can be enteredinto the computer 4 at the beginning, so that the stepping motor 2contains suitable predefinitions for an advance. Furthermore, data aboutthe likely number of labels can also be entered into the computer 4.

In order to perform the calculations, the computer 4 contains imageprocessing software, which is used to calculate the deviations in theposition data between a reference label and a current label.

What is claimed is:
 1. A method for guiding a laser beam over an objectfrom a plurality of identical objects which are conveyed step by stepand substantially periodically past the laser, and wherein said objectshave a varying arrangement relative to the conveying direction, and arestruck at coincident locations by the laser beam, the method comprisingthe following steps: a) arranging a reference object in the image planeof an optical camera; b) recording an image of the reference object bymeans of the camera and displaying the image on a display device; c)marking a point of a line which is to be struck by the laser beam on theimage; d) storing the reference object position data and the markposition data from steps b) and c) in a first memory; e) arranging afurther object in the image plane of the camera; f) recording an imageof the further object with the camera; g) storing the object positiondata of the further object from step f) in a second memory; h)calculating the deviation between the reference object position data inthe first memory and the object position data of the further object inthe second memory; j) calculating the laser position(s) relative to thefurther object on the basis of the deviation in such a way that thelaser strikes the further object at the positions marked in step c); andk) guiding the laser over the further object to the/along the laserposition(s) calculated in step j).
 2. The method as claimed in claim 1,in which method steps e) to )k are carried our repeatedly.
 3. The methodas claimed in claim 1 or 2, in which the objects are textile labelswhich are provided in a textile strip.
 4. The method as claimed in claim3, in which the textile strip is driven by a stepping motor, controlledby a stepping motor control system, and the labels are cut out of thetextile strip by the laser, controlled by a laser control system.
 5. Themethod as claimed in claim 4, in which each step e) is triggered by asignal from the laser control system, which reproduces the completion ofthe step k), to the stepping motor control system.
 6. The method asclaimed in claim 5, in which each step f) is triggered by a signal fromthe stepping motor control system, which reproduces the completion ofstep e), to a camera control system.
 7. An apparatus for guiding a laserbeam over an object from a plurality of identical objects conveyed stepby step and substantially periodically past the laser, and wherein saidobjects have a varying arrangement relative to the conveying direction,and are struck at coincident locations by the laser beam, comprising: atransport device for guiding the objects into the laser operatingregion, a camera whose spatial angle covers the laser operating region,a memory for storing images read out by the camera, a display device fordisplaying the object images from the camera, a marking device formarking a point or a line which is to be struck by the laser beam on areference object image, a computing unit for calculating deviationsbetween reference object position data and further object position datafrom the camera and a control unit for driving the laser on the basis ofthe results from the computing unit to correct for the deviation and toguide the laser beam to a point relative to the further object whichcorresponds in location to the point on the reference object.
 8. Amethod for guiding a laser beam over an object from a plurality ofidentical objects which are conveyed step by step and substantiallyperiodically past the laser, and wherein said objects have a varyingarrangement relative to the conveying direction, and are struck atcoincident locations by the laser beam, the method comprising: obtaininga reference object position data and reference cutting positionsrelative to the reference object to be struck by the laser beams;recording an image of a further object with a camera; obtaining furtherobject position data from the image; calculating deviation between thereference object position data and the further object position data;determining corrected cutting positions for the further object basedupon the reference cutting positions and the deviation; and guiding thelaser beam to the corrected cutting positions.